Our studies have centered on three projects relevant to the host reaction to neoplasia. In the first project membrane proteins from human melanoma cells were radiolabeled and solubilized. These proteins were reacted with antisera from melanoma patients and the immune complexes were co-precipitated and run on SDS gels. Antisera with cytotoxic activity reacted with different melanoma proteins than did antisera with blocking activity. These studies have suggested that a functional dichotomy can be created in the immune response to a tumor by selection of particular determinants from the cell surface. The second project centered on the mechanism of enhancement of a syngeneic murine methyl-cholanthrene-induced sarcoma. The enhancing serum seemed to affect primarily macrophage function. In the third project, cell aggregation and cell adhesion techniques have been used to study the interactions between normal and neoplastic human and murine cells. BIBLIOGRAPHIC REFERENCES: Levy, N.L. and Dawson, J.R. Radiolabeling of immunoglobulin without loss of antibody activity - Use of 14C-phenylisothiocyanate with human cytotoxic antibody. J. Immunol. 116:1526-1531, 1976. Levy, N.L. "Tumor immunology and immunotherapy," In: Zinsser Microbiology, 16th edition (W.K. Joklik and H.P. Willett, eds.), Appleton-Century-Crofts, New York, 1976, pp. 321-332.